A battery module which accommodates plural unit cells in a casing and outputs a predetermined voltage and capacity has been widely used as a power supply for various devices and vehicles. Among them, a battery module in which versatile unit cells are connected to each other in parallel and series and which outputs a predetermined voltage and capacity has been used for various purposes. A decrease in size and weight of the unit cell accommodated in the battery module has been progressed with the high performance. Thus, since the battery module may be decreased in size and weight, the workability when being assembled into the cell pack improves and a degree of freedom when being mounted into a restricted space of a vehicle or the like improves.
On the other hand, it is important to ensure the safety of the battery module as well as the safety of the unit cell with the high-performance of the unit cell accommodated in the battery module. In particular, when a gas is generated due to heat caused by internal short-circuiting or the like and a safety valve is operated so that the hot gas is discharged to the outside of the unit cell, the peripheral unit cell is exposed to the hot gas, which affects even the normal unit cell, so that a series of degradation may occur.
On the contrary, PTL 1 discloses a power supply device which defines a casing accommodating plural unit cells as a cell chamber accommodating the unit cells and a discharge chamber discharging a hot gas discharged from the unit cells by using a partition wall and which includes an exhaust mechanism allowing an opening portion of a safety valve of the unit cell to communicate with the exhaust chamber. With such a configuration, the hot gas discharged from the safety valve of the unit cell may be made to flow into the discharge chamber without flowing into the cell chamber, and may be discharged from the discharge port of the casing to the outside of the casing. Accordingly, the peripheral unit cell may be prevented from being exposed to the hot gas discharged from the abnormal unit cell, and the influence on the normal unit cell may be reduced.
However, in the power supply device disclosed in PTL 1, the plural unit cells are arranged so that the same electrodes face the same direction, and the exhaust chamber is disposed at one electrode. Thus, when the cell units each having plural unit cells connected in parallel to each other are connected in series to each other, a connection lead is needed which has a length corresponding to the length of the cell so as to connect the positive electrode and the negative electrode of the adjacent cell units, and the lead serves as a resistance in the current flowing path.
Further, when the plural cell units are arranged so that the positive electrode and the negative electrode are alternated and the exhaust chamber is provided for each opening portion of the safety valve of the unit cell, the exhaust chamber is provided at both electrode sides of the unit cell. Accordingly, the volume of the battery module increases, and the amount of electric power per unit volume of the battery module reduces.